Tiled is a general purpose tile map editor. It’s built to be easy to use, yet flexible enough to work with varying game engines, whether your game is an RPG, platformer or Breakout clone. Tiled is free software and written in C++, using the Qt application framework.
Talked about the Citrus Engine some time ago but back then only the non-commercial version was free, now it seems the engine is not only free, but open source and with a great 3D support.
Construct 2 launched on Steam! It’s time to build games! Construct 2 is a gamemaker program to make games, there are 3 versions, the first is free (with limitations) and allows the creation of html 5 games without writing a single line of code, the other two versions are for developers to make iPhone, iPad, Android, Windows 8, Windows Phone 8, Facebook, Chrome Web Store, Firefox Marketplace, and the web (HTML5) games. the price for the commercial edition are interesting.
Syntensity, also known as the Syntensity Engine, and previously also called the Intensity Engine, is an open source project that consists of a client, server, and master (metadata) server – everything you need to run your own games or your own virtual world.
Dreemchest is an amazing 2D development engine packed with features. Create beautiful games, graphically-rich apps or eBooks and deploy them across platforms and devices. Making cross-platform and cross-resolution applications is very easy! Build for: Windows, Android, Flash, OS X and iOS.
